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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

272
ALASKAN GLACIER STUDIES
these was already inclined in September, 1910, suggesting that a ploughshare-like basal nose of the glacier was advancing ahead of the visible ice edge. In the intervening area a few rolls of turf were being pushed up and these increased in number during the two months between our 1910 observations.
In the forest there was no audible disturbance that would lead one to suspect that the glacier was advancing, and it was possible to clamber freely among the overturned tree trunks, over the push moraine, and out on the edge of the advancing glacier, whose ice was less splintered and overthrust in July and September, 1910, than in August, 1909. More of the trees seemed to be thrown down by the weight of the glacial moraine material heaped upon their trunks than by the push of the ice itself, therefore falling with their tops away from the ice and afterward being overridden and buried. Some of
FIG. 38.   COLUMBIA. GLAOIEB us SEPTEMBER, 1910. To show advance during 2 months.   Dotted line shows ice edge in June, 1910, see Fig. 82.
the trees, however, were originally overturned by the ice itself and these usually fell toward the glacier, the projecting, buried ice edge pushing their roots forward. They, therefore, lay across the terminal push moraine and in some cases with their tops on the ice itself. Ice seemed to everywhere underlie this terminal push moraine, though in places it was deeply buried.
The terminus of that part of the glacier which ends on the heath between the two forest belts was fronted in August, 1909, by a great push moraine of peat and turf with a few tree trunks, some bowlders, and a little gravel and till. This push moraine rose twenty to twenty-five feet above the heath on the south, which sloped gradually to the shores of a small pond. The ice-contact face of the push moraine sometimes had a depression between it and the ice which was due to the thrust, not to melting, for the grasses on the inner slope had not been destroyed. The shoving up of the push moraine was evidently due mainly to the powerful ploughing of the glacier foot and the thrusting forward of the soil.